After a wild and passionate youth, YouTube and Ning have both announced they're adopting a policy of abstinence. Heck, they might even join a convent. Why? Money, of course.

Ning is saying sayanora to its Red Light District, the adult section of the DIY social networking site. Come January 1 they're kicking the call girls to the curb and putting a crimp on pimps. (Memo to Marc Andreessen: I mean that metaphorically -- please don't sue me.)

YouTube has just announced new policies designed to keep quasi-smutty videos from rising to the top of its pages. The underlying reason in both cases is these sites desperately want to win the hearts of mainstream advertisers, who don't want their ads appearing in the same neighborhood as The Pussykat Theater and Wicked Wanda's House of Devilish Delites.

YouTube just released new rules about what it considers "sexually suggestive" videos that are comical in their prudishness. Besides nudity and actual sex, videos may be age-restricted if they “feature individuals in minimal or revealing clothing... [or] if they're intended to elicit a sexual response.”

Other considerations?

Whether breasts, buttocks, or genitals are the "focal point" of the video. So much for the BootyTown Channel.

Whether the video is set in a location "associated with sexual activity, such as a bed." Because as we all know, people only have sex in bed.

Actions that suggest "a willingness to engage in sexual activity." Ideally, both the video's creators and its viewers will have been married to each other for at least 10 years, so the issue will never come up.

Minimal clothing is acceptable, but only in appropriate contexts. That micro-thong bikini? No sweat if you're poolside, but better grab a towel before you step inside the kitchen.

In other words, to comply with YouTube's age-restricted standards you'd pretty much have to be dressed as a nun sitting in an uncomfortable chair with your legs crossed while thinking pure thoughts.

Talk about kinky.

In practical terms these restrictions do nothing to protect the youth of America from having their sensibilities warped by hot booties and thong bikinis. YouTube merely requires you to create an account and say "Yes, I am 18 or older" before showing you the goods. That's just a joke, and not a funny one.

The bigger effect is that YouTube is tweaking its algorithms to bury all that highly popular yet suggestive stuff down in the search results. The Vicar is on the doorstep and they've got 30 seconds to stash those copies of Barely Legal in the basement.

It's no secret that, like the Internet itself, YouTube used sex to reach critical mass. The most popular v-bloggers are invariably the ones who display their assets, and I don't mean their stock portfolios. So now, after fooling around with the neighborhood strumpet for four years, YouTube wants to toss her aside and marry the Vicar's daughter.

Understandable? Sure. Hypocritical? Just a wee bit.

It's a cliché that the Web was built on the back of the beast with two backs. Some 15 years later, just how much of the Net is porn today varies wildly depending on whom you ask. Optenet, a content filtering service based in Spain, released a survey in September that claimed roughly 35 percent of Web sites contain pornographic content. (It made other, more troubling claims that I'll talk about in a future blog post.)

That survey has many problems, not the least of which is that it underestimates the size of the Internet by a few orders of magnitude (in my humble, not-a-professional-statistician opinion). I asked Charles Renert, senior director of advanced content research at Websense, how much of the Net is porn. His best guess is that the percentage of porn sites is in the single digits. (He also agrees that Optenet's estimate of the Net's size is way off.) But Renert says that yardstick is irrelevant. What matters is where people go. And about 80 percent of the Net's traffic goes to the top 100 sites (including YouTube), says Renert.

Though porn is increasingly less of a presence on the Net -- and increasingly less profitable for its purveyors, due to the explosion of free adult content -- it helped spur the adoption of ecommerce, online payment systems, broadband connections, streaming and live video, and much more. I'll be writing more about this soon here and elsewhere, so stay tuned.

Ning and YouTube might try to bury their shady past, but they can't escape it. The real question is whether they can thrive -- or even survive -- without it.